/usr/bin/mono-service is in mono-4.0-service 4.6.2.7+dfsg-1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | #!/bin/sh
args=""
assembly=
debug=false
while test x$1 != x; do
	case $1 in
		-[ldnm]:*) args="$args$1 " ;;
	        --debug) debug=true ;;
	        --no-daemon) debug=true ;;
		*) assembly=$1;  args="$args$assembly ";;
	esac
	shift
done
if test x$assembly = x; then
	echo You must specify at least the assembly name
	echo 
	echo "Usage is: $0 [options] service"
	echo 
	echo '    -d:<directory>         Working directory'
	echo '    -l:<lock file>         Lock file (default is /tmp/<service>.lock)'
	echo '    -m:<syslog name>       Name to show in syslog'
	echo '    -n:<service name>      Name of service to start (default is first defined)'
        echo '    --debug                Do not send to background nor redirect input/output'
        echo '    --no-daemon            Do not send to background nor redirect input/output'
	echo 
	echo Controlling the service:
	echo 
	echo '    kill -USR1 `cat <lock file>`    Pausing service'
	echo '    kill -USR2 `cat <lock file>`    Continuing service'
	echo '    kill `cat <lock file>`          Ending service'
	echo 
	exit 1
fi
export MONO_DISABLE_SHM=1
if $debug; then
   exec /usr/bin/mono $MONO_OPTIONS /usr/lib/mono/4.5/mono-service.exe $args
else
   exec /usr/bin/mono $MONO_OPTIONS /usr/lib/mono/4.5/mono-service.exe $args </dev/null >/dev/null 2>&1 &
fi
 |